Mercruiser 3.0 Valve Adjustment question

March 25th, 2020, 04:27 PM

First post here and first boat. 1993 sea ray 170 bow rider. I bought this boat knowing it needed some work but it appeared in good shape. Water tested boat and found water in bilge and found a tear in the bellows so replaced all bellows and shift cable. Boat had been sitting for 4 years so drained the fuel changed oil and filter and spark plugs as well first outing went great second outing was doing around 30 and the motor stopped instantly and would not turn over so got a tow brought the boat home and determined the outdrive had sprung a leak and enough oil leaked out to ruin the upper gear case causing it to seize up. so i purchased a outdrive locally and installed it. I have put around 20 hours on the boat and it runs great however after running the boat across the lake for extended periods at no more than 3200-3800 rpm when idling back into the marina there is a distinctive tap that sounds like a lifter or rocker arm so i pulled the valve cover and everything looks spotless and all lock nuts appear to be equally tightened. so the Mercruiser manual dated 1999 says zero lash and 3/4 turn the gm 3.0 manual dated 1994 says 1 full turn? Serial number above starter says F068675

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Firstly the 3.0 is well known and famous for being a great wee work horse...but just as famous for being a very rough sounding engine when warm and oil is thin especially. Well known for a very distinctive tapping noise at certain rpm. Many will agree with me here.

The other possibility is that if it’s doing it at rpm around 900-1300 rpm or close...it could be your flappers in the exhaust too.

pretty sure that one of the above might well be the issue.

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Yes it only seems to do it after being out for a few hours and then during no wake speed coming back into the marina I did not know there was an exhaust flapper this could very well be what I'm hearing. I'm glad I took the valve cover off anyway as it was sipping a little oil at the rear of the head so have a new gasket here tomorrow morning. I will go ahead and check all the valves while I have the cover off just to be sure. Thank you for the info.

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In looking at all of the lock nuts on top of the rocker arms they all appear to have the same exact amount of thread from the stud in the head I'm debating whether to loosen them all up just to check them as I am concerned they may lose some of their tension on the stud. Do you think this would be a factor? I'm trying to post a picture however it tells me to file size must be under 2mb and the lowest I can set my camera is 9 MP so the files still come out too large

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I have never heard of the head having to be re-torqued on the 3.0 unless you removed it or have some other reasoning. As for your other question someone else will have to chime in. I do not want to tell you wrong information. Qhboy is right, that engine is known for the tapping. Had one for years before current boat, awesome dependable little engine, but that d#^$ tapping noise would drive me crazy. Like you after running and the engine is warm. Checked my lash and everything was good. Never figured it out as it ran really good (thanks to everyone here).

2014 Mercruiser 4.3 mpi ect - SN 2A176701

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Okay cool I'm going to leave it be then everything looks good I replace the thermostat while I was in here as the motor was not getting up past 100°. When I got the boat the guy gave me two propellers and I later found out that it had a V6 outdrive on it with the 1.81 ratio now that I have replace the Outer Drive and has a 1.98 and with the 19 propeller it will only get up to 4200 RPM with 2 people and two dogs. I read somewhere on here that it needs to be getting closer to the Max RPM 4600. When I put the 17 propeller on the RPMs go over 4,800 so I'm going to put the other 19 propeller back on. You think it would be an issue the motor only reaching 4200 and 39 miles an hour or would this be stressing the motor out. I never run it for Full Throttle more than 30 seconds

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X3 on the good advice given by Qbouy and Andrew - 3.0s are noisy and clacky... but very reliable with basic maintenance

I think you maybe be over thinking it. Running a 40 weight oil or adding Lucas can help quiet it, so can more beer and a louder radio...

my advice slow your roll before you turn too many wrenches. listen for the exhaust flappers in the down pipe off the exhaust elbow. Maybe post a vid so others can hear the noise.... likely your engine is just fine - what’s your oil pressure run hot at speed? If that’s ok you’re probably fine

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Okay next time I'm out on the water I will take a video. I'm sure it's fine as well it runs real good I just wanted to check as it sounds like it's coming from the top end. Unfortunately they have shut down the entire Lake so I may be waiting a while until this virus hysteria subsides. Thanks for all the advice guys I'm sure the more I get to know the boat the more questions I will have.

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Okay cool I'm going to leave it be then everything looks good I replace the thermostat while I was in here as the motor was not getting up past 100°. When I got the boat the guy gave me two propellers and I later found out that it had a V6 outdrive on it with the 1.81 ratio now that I have replace the Outer Drive and has a 1.98 and with the 19 propeller it will only get up to 4200 RPM with 2 people and two dogs. I read somewhere on here that it needs to be getting closer to the Max RPM 4600. When I put the 17 propeller on the RPMs go over 4,800 so I'm going to put the other 19 propeller back on. You think it would be an issue the motor only reaching 4200 and 39 miles an hour or would this be stressing the motor out. I never run it for Full Throttle more than 30 seconds

. I used to run a 19” with the correct 1.98 drive on mine-1991 sea ray 170. Used a 17” for skiing, lightly loaded would hit the rev limiter with the 17” prop. Might verify your tach as I’d think you’d be more than 4200 rpm at 38 mph, wouldn’t expect much more than 40 mph . Is speed gps or the dash?

4200 is low 4400-4800 is a good rpm at wot. If you really are at 4200 with a 19”, run the 17” better to be a little under propped vs over propped.

Full throttle is ok, ran mine very hard for many years (20) towing skiers and tubes, still ran very well when I sold it.

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Good info Scott. I will try and dig up one of my old analog engine analyzers from back in the day to verify rpm. I did a compression test all cylinders were equal at 140 however there seems to be a good bit of oil mist around the valve cover vent to carb. I was leery to run full throttle for extended distances as we end up in some pretty remote places sometimes. Speed was on a GPS speedometer app as the factory speedo reads 10 mph low. Oil pressure is in the high 30s at idle and low 40s at 4000 RPM. What grade of fuel did you used to run?

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Just 87 regular pump gas is all you need. With the oil from the valve cover vent on the flame arrester, they all do that as it is a vent and if you overfill there will be a lot more. Just grab a can of carb cleaner and spray off the flame arrester than let it DRY before reinstalling and running the engine. What state do you live in? I am in Oklahoma and they closed non essential businesses but they are pushing the outdoors and people going to the lakes.

2014 Mercruiser 4.3 mpi ect - SN 2A176701

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In looking at all of the lock nuts on top of the rocker arms they all appear to have the same exact amount of thread from the stud in the head I'm debating whether to loosen them all up just to check them as I am concerned they may lose some of their tension on the stud. Do you think this would be a factor? I'm trying to post a picture however it tells me to file size must be under 2mb and the lowest I can set my camera is 9 MP so the files still come out too large

read the photo posting tutorial in the rules and guidelines forums.

you have to re-size the pics, simplest way is to email them to yourself and pic 25%

I ran a 19P, a 17P and a 15P prop on my 3.0 depending on what I was doing.

with a 3.0, keep the ignition timing spot on. too much ignition advance and it will rattle and ping like crazy